Fire detector devices may be designed to actuate an alarm by closing or opening a circuit on the happening of either one, or both, of two events--when the rate of rise of the temperature of the ambient atmosphere exceeds a predetermined prescribed standard, for example, the 15F.degree. per minute standard set by Underwriter Laboratories of Canada and Underwriter Laboratories Inc. of the United States, and/or when the ambient temperature exceeds a predetermined fixed temperature.
These detectors must also operate in all environmental conditions, for example, extremes of humidity, variations of heat and cold, and acidic or alkaline vapour mediums.
The necessity for such operation has been recognized by various Governmental and independent examining bodies, and standards have been set which the devices must meet or exceed. One such body is the Fire Insurer' Research and Testing Organization (FIRTO for short) of the United Kingdom, who as part of its testing program, has prescribed that such fire detectors must pass a sulphuric acid environment test. This test requires that the fire detector sit in a sulphuric acid environment for a predetermined time and thereafter, still be operable. However, no fire detector that vents to the atmosphere tested with the rate of rise feature has remained operable after the time period spent in the sulphuric acid vapour medium. The reason lies in the construction of the vented detector incorporating the rate of rise feature. The chamber between the shell and diaphragm and diaphragm and base must be vented to atmosphere to permit normal atmospheric expansion due to temperature fluctuations without actuating the alarm.
The vent apertures if left unprotected in the acidic environment, permit the acidic environment to be drawn into the chambers when the detector is breathing during normal temperature fluctuations, corroding the electrical contacts.
Surrounding the vents with a wall and covering the wall created with a closure cap, providing a small vent hole in the cap wall or between the cap and wall only accentuates the problems of corrosion. The small vent hole, it is thought, acts as a pump drawing in and exhausting substantial amounts of acidic vapour through the small vent hole and permits condensation of the vapour, thereby trapping the liquid acid in the contact area.
Additionally, during the tests, some heat collecting fins on certain fire detectors were also attacked by the corrosive vapour and lost their temperature sensitivity due to the formation of a residue on the fin as a result of the reaction between the metal fin and fusible link (if exposed--holding the plunger), and the sulphuric acid vapour.
Where the fin and ferrule were combined in one piece, in the detector, the fin was not only attacked by the vapour, but the fin could not be manufactured of a large diameter at reasonable cost. However, it is desirable to manufacture fins of large diameter for enhanced temperature sensitivity. Where attempts have been made to make the fin-furrel combination from two components, with the fin of large diameter, the union has not yielded a satisfactory result. Particularly, where the two pieces are to be joined, they must be "married" to effect maximum metal contact at the joint for effective heat transfer between the components, to the fusible link.
It is therefore, an object of this invention to provide an improved fire detector and structural components useful therefor.
It is a further object of this invention to provide an improved fire detector vented to atmosphere having a rate of rise feature suitable for use in an acidic vapour medium.
It is a further object of the invention to provide an improved detector having an improved heat fin for the collection and effective transfer of heat to the fusible link holding the plunger for release at a fixed predetermined temperature (the fusion temperature of the fusible link).
Further and other objects of the invention will be realized by those skilled in the art from the following summary of the invention and detailed description of preferred embodiments thereof.